fix: replace stale magic DNS records on IP change (#1906)

Magic DNS updates are full snapshots, so appending routes keeps old IPs and returns duplicate A records. Replace each client's previous routes on update and add a regression test to ensure hostname resolution keeps only the latest IP.

easytier/src/instance/dns_server/server_instance.rs

@@ -140,6 +140,19 @@ impl MagicDnsServerInstanceData {
         }
     }
 
+    async fn keep_zone_authoritative(&self, zone: &str) {
+        if let Err(e) = self
+            .update_dns_records(std::iter::empty::<&Route>(), zone)
+            .await
+        {
+            tracing::error!(
+                "Failed to keep DNS zone {} authoritative after route prune: {:?}",
+                zone,
+                e
+            );
+        }
+    }
+
     fn do_system_config(&self, zone: &str) -> Result<(), anyhow::Error> {
         if let Some(c) = &self.system_config {
             c.set_dns(&OSConfig {
@@ -183,10 +196,25 @@ impl MagicDnsServerRpc for MagicDnsServerInstanceData {
             return Err(anyhow::anyhow!("No remote addr").into());
         };
         let zone = input.zone.clone();
-        self.route_infos
+        let remote_addr: url::Url = remote_addr.clone().into();
-            .entry(zone.clone())
+        let mut zone_removed = false;
-            .or_default()
+
-            .insert_many(remote_addr.clone().into(), input.routes);
+        if let Some(mut routes_by_addr) = self.route_infos.get_mut(&zone) {
+            routes_by_addr.remove(&remote_addr);
+            if !input.routes.is_empty() {
+                routes_by_addr.insert_many(remote_addr, input.routes);
+            }
+            zone_removed = routes_by_addr.is_empty();
+        } else if !input.routes.is_empty() {
+            let mut routes_by_addr = MultiMap::new();
+            routes_by_addr.insert_many(remote_addr, input.routes);
+            self.route_infos.insert(zone.clone(), routes_by_addr);
+        }
+
+        if zone_removed {
+            self.route_infos.remove(&zone);
+            self.keep_zone_authoritative(&zone).await;
+        }
 
         self.update().await;
         Ok(Default::default())
@@ -438,11 +466,19 @@ impl RpcServerHook for MagicDnsServerInstanceData {
             return;
         };
         let remote_addr = remote_addr.into();
+        let mut removed_zones = vec![];
         for mut item in self.route_infos.iter_mut() {
             item.value_mut().remove(&remote_addr);
+            if item.value().is_empty() {
+                removed_zones.push(item.key().clone());
+            }
+        }
+        for zone in &removed_zones {
+            self.route_infos.remove(zone);
+        }
+        for zone in removed_zones {
+            self.keep_zone_authoritative(&zone).await;
         }
-        self.route_infos.retain(|_, v| !v.is_empty());
-        self.route_infos.shrink_to_fit();
         self.update().await;
     }
 }

easytier/src/instance/dns_server/tests.rs

@@ -23,6 +23,8 @@ use crate::peers::peer_manager::{PeerManager, RouteAlgoType};
 use crate::peers::create_packet_recv_chan;
 use crate::proto::api::instance::Route;
 use crate::proto::common::NatType;
+use crate::proto::magic_dns::{MagicDnsServerRpc as _, UpdateDnsRecordRequest};
+use crate::proto::rpc_types::controller::{BaseController, Controller as _};
 
 pub async fn prepare_env(dns_name: &str, tun_ip: Ipv4Inet) -> (Arc<PeerManager>, NicCtx) {
     prepare_env_with_tld_dns_zone(dns_name, tun_ip, None).await
@@ -78,8 +80,9 @@ pub async fn check_dns_record(fake_ip: &Ipv4Addr, domain: &str, expected_ip: &st
             rr::RecordType::A,
         )
         .await
-        .unwrap();
+        .unwrap_or_else(|e| panic!("DNS query failed unexpectedly for domain '{domain}': {e}"));
-    drop(background_task);
+    background_task.abort();
+    let _ = background_task.await;
 
     println!("Response: {:?}", response);
 
@@ -91,6 +94,29 @@ pub async fn check_dns_record(fake_ip: &Ipv4Addr, domain: &str, expected_ip: &st
     );
 }
 
+pub async fn check_dns_record_missing(fake_ip: &Ipv4Addr, domain: &str) {
+    let stream = UdpClientStream::builder(
+        SocketAddr::new((*fake_ip).into(), 53),
+        TokioRuntimeProvider::default(),
+    )
+    .build();
+    let (mut client, background) = Client::connect(stream).await.unwrap();
+    let background_task = tokio::spawn(background);
+    let response = client
+        .query(
+            rr::Name::from_str(domain).unwrap(),
+            rr::DNSClass::IN,
+            rr::RecordType::A,
+        )
+        .await
+        .unwrap_or_else(|e| {
+            panic!("DNS query for missing record failed unexpectedly for domain '{domain}': {e}")
+        });
+    background_task.abort();
+    let _ = background_task.await;
+    assert!(response.answers().is_empty(), "{:?}", response.answers());
+}
+
 #[tokio::test]
 async fn test_magic_dns_server_instance() {
     let tun_ip = Ipv4Inet::from_str("10.144.144.10/24").unwrap();
@@ -181,3 +207,119 @@ async fn test_magic_dns_runner() {
         t.await.unwrap();
     }
 }
+
+#[tokio::test]
+async fn test_magic_dns_update_replaces_records_for_same_client() {
+    let tun_ip = Ipv4Inet::from_str("100.100.100.0/24").unwrap();
+    let ctx = get_mock_global_ctx();
+    ctx.set_hostname("test1".to_string());
+    ctx.set_ipv4(Some(tun_ip));
+
+    let (s, _r) = create_packet_recv_chan();
+    let peer_mgr = Arc::new(PeerManager::new(RouteAlgoType::Ospf, ctx, s));
+    peer_mgr.run().await.unwrap();
+    replace_stun_info_collector(peer_mgr.clone(), NatType::PortRestricted);
+
+    let fake_ip = Ipv4Addr::from_str(MAGIC_DNS_FAKE_IP).unwrap();
+    let dns_server_inst = MagicDnsServerInstance::new(peer_mgr.clone(), None, tun_ip, fake_ip)
+        .await
+        .unwrap();
+
+    let mut ctrl = BaseController::default();
+    ctrl.set_tunnel_info(Some(crate::proto::common::TunnelInfo {
+        tunnel_type: "tcp".to_string(),
+        local_addr: None,
+        remote_addr: Some(crate::proto::common::Url {
+            url: "tcp://127.0.0.1:54321".to_string(),
+        }),
+    }));
+
+    dns_server_inst
+        .data
+        .update_dns_record(
+            ctrl.clone(),
+            UpdateDnsRecordRequest {
+                zone: DEFAULT_ET_DNS_ZONE.to_string(),
+                routes: vec![Route {
+                    hostname: "test1".to_string(),
+                    ipv4_addr: Some(Ipv4Inet::from_str("8.8.8.8/32").unwrap().into()),
+                    ..Default::default()
+                }],
+            },
+        )
+        .await
+        .unwrap();
+
+    dns_server_inst
+        .data
+        .update_dns_record(
+            ctrl,
+            UpdateDnsRecordRequest {
+                zone: DEFAULT_ET_DNS_ZONE.to_string(),
+                routes: vec![Route {
+                    hostname: "test1".to_string(),
+                    ipv4_addr: Some(Ipv4Inet::from_str("1.1.1.1/32").unwrap().into()),
+                    ..Default::default()
+                }],
+            },
+        )
+        .await
+        .unwrap();
+
+    let dns_records = dns_server_inst
+        .data
+        .get_dns_record(
+            BaseController::default(),
+            crate::proto::common::Void::default(),
+        )
+        .await
+        .unwrap();
+    let zone_records = dns_records.records.get(DEFAULT_ET_DNS_ZONE).unwrap();
+    let a_records = zone_records
+        .records
+        .iter()
+        .filter_map(|record| match record.record.as_ref() {
+            Some(crate::proto::magic_dns::dns_record::Record::A(a))
+                if a.name == "test1.et.net." =>
+            {
+                Some(a)
+            }
+            _ => None,
+        })
+        .collect::<Vec<_>>();
+
+    assert_eq!(a_records.len(), 1, "{a_records:?}");
+    let resolved_ip = Ipv4Addr::from(a_records[0].value.unwrap_or_default());
+    assert_eq!(resolved_ip, Ipv4Addr::new(1, 1, 1, 1));
+
+    let mut ctrl = BaseController::default();
+    ctrl.set_tunnel_info(Some(crate::proto::common::TunnelInfo {
+        tunnel_type: "tcp".to_string(),
+        local_addr: None,
+        remote_addr: Some(crate::proto::common::Url {
+            url: "tcp://127.0.0.1:54321".to_string(),
+        }),
+    }));
+
+    dns_server_inst
+        .data
+        .update_dns_record(
+            ctrl,
+            UpdateDnsRecordRequest {
+                zone: DEFAULT_ET_DNS_ZONE.to_string(),
+                routes: vec![],
+            },
+        )
+        .await
+        .unwrap();
+
+    let dns_records = dns_server_inst
+        .data
+        .get_dns_record(
+            BaseController::default(),
+            crate::proto::common::Void::default(),
+        )
+        .await
+        .unwrap();
+    assert!(!dns_records.records.contains_key(DEFAULT_ET_DNS_ZONE));
+}